Users of computer systems, or related appliances such as laptops, tablets, smart phones, etc., enter information through a keyboard, cursor click device such as a mouse, or other interface device that involves interaction between the user and displayed information. Another person (hereinafter referred to as “unauthorized person,” “eavesdropper,” “trojan,” or the like) may observe the user's data entry, and learn information that the user would prefer to keep private. Such information may include system passwords, or other information whose confidentiality has value to the user. Because many types of electronic computer-based appliances are small, lightweight and portable, unauthorized persons have many opportunities to observe a user's private information. Also, surveillance software such as keylogger, screenlogger, and Trojan horse software may be provide unauthorized persons with access to a user's private information entered through the user interface.